Not true. Some people have some level of immunity if they previously had a Coronavirus like SARS or MERS. And as far as it being "deadlier" than the flu, we have a ways to go before truly determining that. To get an accurate fatality rate, we first need to have an accurate number of people who have or had COVID-19, and that just isn't possible yet due to a serious lack of available testing. It is suspected a lot of people have had it but were never confirmed, so therefore not counted. Don't let the media numbers fool you.
The best actual defense against this virus is herd immunity. Besides the elderly and immune compromised folks, if most others were allowed to be exposed to this virus, get it, get through it, and move on with life...we would be much better off. The vast majority of people who get this, recover. Then, those people build immunity to it...then...the virus isn't able to spread.
Everything that's going on now...social distancing, all the shutdowns, etc, is purely only delaying the inevitible. It's all to not overwhelm the hospitals with sick people. It won't stop us from eventually being exposed because that is going to happen at one point or another. We can't stay socially distant and keep businesses shut down forever. It's already damaging enough.